Johannesburg, also known as eGoli (place of gold), is the largest and most populous city in South Africa. Johannesburg is the site of a large-scale gold and diamond trade due to its location on the mineral-rich Witwatersrand range of hills. Johannesburg is also served by O.R. Tambo International Airport, the largest and busiest airport in Africa and a gateway for international air travel to and from the rest of southern Africa.